Fluid subdividing and filling device, and piston and clamp used in the same

ABSTRACT

A fixing member is fixed on a structure for moving a piston forward and backward. Piston clamps rotatably face the fixing member, and an elastic body biases the piston clamps forward. A holding unit for holding detachably the rear end of the piston shaft is formed on both ends of the piston clamps. Tapers expanding gradually in the forward direction are formed on the surface opposite to the top end of the holding unit. An elastic body to which the rear end of the piston shaft is brought into contact. An opening member with tapers guides upward the tapers at the top of the piston clamp holding unit. The fixing member moves forward causing the piston clamps to move forward further. The piston shaft compresses the elastic body. The tapers at the top of the piston clamps holding unit open and the piston shaft and the piston clamps separate.

BACKGROUND OF THE INVENION

This invention relates of fluid subdividing and filling device for use of filling, into canned food or a vacuum-pack bag, ingredients-contained soup or the like, or for use of subdividing by a fixed quantity and piston and clamp used in the same.

RELATED PATENTS

Japanese Paten No. 3267964

DESCRIPTION OF THE PRIOR ART

For packing an ingredient-containing soup or the kike such as curry, minestrone, pork soup, stew in a can or a vacuum packaging bag, conventionally, two steps, i.e. step for filling an ingredient and step for filling soup have been used. Therefore, there poses a problem that working efficiency is not enhanced.

For solving such a problem as noted above, the present applicant has developed a fluid subdividing and filling device capable of subdividing and filling an ingredient and soup liquid together, and applied for patent, which has already been patented (for example, see Japanese Paten No. 3267964).

In the above-described conventional fixed quantity valve system, an ingredient and soup are taken from the top of a cylinder, cutting-out is done by a rotary valve incorporated into the inside diameter of the cylinder, it is rotated at 180° C., the taken opening is adjusted to an opening under the cylinder, and thereafter, the taken ingredient-contained soup is pressed out by a piston to thereby take a soup into a container.

The piston incorporated into the inside diameter of the rotary valve is pulled to a fixed position from the forward end to thereby form a space for cylindrical volume, and the soup taken into the space can be the fixed capacity. If the amount of pulling the piston is always constant, the cylindrical space will wholly be the fixed volume.

Further, where the conventional fixed quantity discharge cutout valve is mounted on the soup server body by the cartridge system, a method is employed to fall it obliquely once when mounted, and insert the rear end of the piston shaft into a piston receiving fixture.

The above-described device receives very high evaluation because the ingredient-contained soup can be subdivided into a fixed volume easily. However, as a problem, there was found a problem of fitting of the rotary valve incorporated into the inside diameter of the cylinder body.

That is, if fitting is gentle, liquid leakage occurs along the circumference of a fitting portion, and if fitting is hard, large torque is necessary to rotate the rotary valve, sometimes resulting in the cause of occurrence of scuffing. Particularly leading to difficulty, it is difficult to remove the rotary valve to be overhauled and washed after completion of day's work.

In addition, thermal expansion occurs depending on the thermal transmission generated when soup is heated, and since the fitting condition changes, a very troublesome problem occurs. That is, an operator's handling becomes worse.

For improving the operator's handling, the conditions are provided so as to make fitting as gentle as possible, and so that even if the thermal expansion should occur, gentleness remains unchanged. However, there is a problem that if fitting is gentle, soup liquid turns down along the circumference to produce a liquid leakage from the lower discharge portion.

Further, conventionally, for sealing a piston, an O-ring is used, an axial seal can be done positively by using the O-ring, but a motor that drive torque of pushing and pulling is 15 W capacity was necessary. There was a problem that much electric energy therefor is necessary.

Further, since a hopper and a fixed quantity discharge valve are connected to a piston shaft shown in FIG. 1, total weight in the state that soup is filled is about 10 kg. In inserting this 10 kg fallen obliquely and into a piston receiving fixture, it is very difficult work for female.

OBJECTS AND SUMMARY OF THE INVENTION

The present inventions described in Claims 1 to 3 out of the inventions have their object to provide a fluid subdividing and filling device in which even fitting is made gentle, soup liquid is not leaked from a fitting portion and a discharge portion.

Further, the present invention described in Claim 4 has its another object to provide a piston wherein soup liquid is hard to be leaked from a fitting portion and drive torque for pushing and pulling is made small.

Further, the present invention described in Claim 7 has its another object to provide a fluid subdividing and filling device wherein a fixed quantity discharge valve is placed on a server set bed to make automatically connectable.

Furthermore, the present invention described in Claim 8 has its another object to provide a clamp wherein a fixed quantity discharge valve is placed on a server set bed to make automatically connectable.

The invention described in Claim 1 out of the inventions in accordance with the aforementioned objects provides a fluid subdividing and filling device in which a piston is moved backward to fill a fluid to be subdivided and filled into a cylinder, and the piston is moved forward to discharge said fluid, characterized in that a rear end portion of a piston body fitted slidably in said cylinder is formed to be somewhat smaller so that a short cylindrical seal is fitted, said short cylindrical seal is formed to have a taper in which an end inner circumference of a short cylindrical plate is spread open, a shoulder portion of the cylinder in contact with said taper is formed in a taper that rises in the forward direction, a short cylindrical seal holder is fitted from backward of said short cylindrical Teflon seal, said short cylindrical Teflon seal is pressed forward, whereby the extreme end of said short cylindrical Teflon seal is projected somewhat from a piston body outer circumference.

The fluid subdividing and filling device preferably includes a fixed quantity cut-down pump body having an suction opening in communication with an lower-end opening of a liquid food accommodating container for subdividing and filling and a discharge opening to a subdividing and filling container, a cylinder turnably fitted in the fixed quantity cut-down pump body, a piston slidably fitted in the cylinder, and a through-hole formed in the cylinder, wherein rotation of the cylinder and advance/backward movement of the piston are coupled so that the through-hole of the cylinder is communicated with the suction opening of the fixed quantity cut-down pump body, the piston moves back to fill a fixed quantity of liquid food into the cylinder whereas when the through-hole of the cylinder is communicated with the discharge opening of the apparatus body, the piston advances to discharge liquid food from the discharge opening communicated(claim 2). In this case, two through holes may be formed in the cylinder, one formed in the lateral side of the cylinder connected with the suction opening and another formed at the top of the cylinder connected with the discharge opening.

The leakage of liquid soup from the discharge opening may be effectively prevented by fixing a cylindrical Teflon seal formed in a curved surface whose top can be brought into tight contact with the cylinder on the discharge outlet of the device proper to bring the top opening of the Teflon seal into tight contact with the cylinder and covering the through hole (claim 3).

A rear end portion of a piston body fitted slidably in said cylinder is formed to be somewhat smaller so that a short cylindrical seal is fitted, said short cylindrical seal is formed to have a taper in which an end inner circumference of a short cylindrical plate is spread open, a shoulder portion of the cylinder in contact with said taper is formed in a taper that rises in the forward direction, a short cylindrical seal holder is fitted from backward of said short cylindrical Teflon seal, said short cylindrical Teflon seal is pressed forward, whereby the extreme end of said short cylindrical Teflon seal is projected somewhat from a piston body outer circumference. In this way, when the piston is pushed, the protruding Teflon seal stands up making it difficult for the soup liquid to leak, and when it is pulled, the Teflon seal falls enabling to reduce driving torque at the same time (claim 4).

The formation of the top surface of the piston body into a convex gently curved shape enables to avoid the top surface of the piston and the top surface of the cylinder from entering into a close contact, and during this period it will be possible to avoid soup ingredients from getting pinched and to reduce driving torque (claim 5).

The degree of contact between the Teflon seal and the cylinder may be easily adjusted just like a wedge by forming a concave tapped hole in the rear end surface of the piston body, fitting the top of the piston shaft into the tapped hole, screwing and tightening a nut fitted on the piston shaft, and thus pressing the rear end surface of the seal holder fitted on the piston shaft (claim 6).

In a fluid subdividing and filling apparatus wherein the cylinder is filled with a fluid destined to be subdivided and filled by the backward movement of the piston and the fluid is discharged by the forward movement of the piston, the fixed quantity discharge valve and the soup server may be easily detached and attached, when the device includes a fixing member fixed on the means for making the piston move forward and backward, piston clamps fixed rotatably facing the fixing member, an elastic body giving impetus to the piston clamps forward in the closing direction, a holding unit for holding detachably the rear end of the piston shaft formed on both extreme ends of the piston clamps, a taper expanding gradually forward formed in the surface facing the top of the holding unit, and an elastic body to which the rear end of the piston shaft enters into contact directly or through other members, an opening member with a taper guiding upward opening the taper at the top of the piston clamp holding unit, and wherein the forward movement of the fixing member results in the forward movement of the piston clamps further forward beyond the end limit of the forward movement and results in the compression of the elastic body by the piston shaft, and the top taper of the holding part of the piston clamp, being guided in contact with the taper of the opening member, opens and thus the piston shaft and the piston clamps separate. (claim 7).

The piston shaft and the means for making the piston move forward and backward may be easily detached by the provision of a fixing member fixed on the means for making the piston move forward and backward, a piston clamp fixed rotatably facing the fixing members, an elastic member giving forward impetus to the piston clamp in the closing direction, a holding unit for holding detachably the rear end of the piston shaft formed on both top ends of the piston clamps, a taper expanding gradually forward formed on a surface opposite to the top end of the holding unit, an elastic body to which the rear end of the piston shaft is brought into contact directly or through other members, an opening member with a taper guiding upward the top taper of the piston clamp holding unit to open, and the adoption of a structure wherein a forward movement of the fixing member resulting in the forward movement of the piston clamp further forward beyond the end of the forward movement course results in the compression of the elastic body by the piston shaft, and the taper at the end of the piston clamp holding unit, guided in contact with the taper of the opening member, opens resulting in the separation of the piston shaft and the piston clamp (claim 8).

As for the means for making the piston move forward and backward, it is preferable to adopt a rack gear engaged with a pinion fixed on the rotary shaft of the motor (claim 9)

It is preferable to fix rotatably the piston clamp and the fixing member backward from the center of the piston clamp and place an elastic body giving impetus to the piston clamp forward in the closing direction taking the fixing point as the supporting point between the piston clamps behind the supporting point and the fixing member (claim 10).

It is preferable to form a housing unit for housing an elastic body in front of the fixing member, to provide a piston shaft pressure bar to which impetus is given by the elastic body in the opening in front of the housing unit, and the rear end of the piston shaft is located in such a way that it may be brought into contact with the piston shaft pressure bar.

According to the invention described in claim 1, the protrusion of the cylindrical Teflon seal stands up when the piston is pushed, and the same falls when the piston is pulled. Therefore, the present invention can eliminate the leakage of soup liquid in the shaft direction and reduce driving torque (6.5 w in the embodiment described after). In addition, the cylindrical Teflon seal plays the role of a hook and therefore eliminates the leakage of soup liquid in the shaft direction, and moreover when the work is completed, the piston can be easily pulled out of the cylinder by pulling the protrusion of the Teflon seal.

According to the invention described in claim 3, in addition to the effect described above, it is possible to completely eliminate the leakage of soup liquid from the discharge outlet irrespective of the type of soup liquid by covering the through hole (discharge outlet) of the rotating cylinder by the cylindrical Teflon seal, a method that had never been used before.

And according to the invention described in claims 7 and 8, the clamps can be detached and attached simply by making them move forward and backward, and therefore they can be detached and attached automatically. Thus, their detaching and attaching operation can be greatly simplified as compared with the prior method of detaching and attaching and therefore the working efficiency is greatly improved.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic sectional view showing the prior method of connecting the fixed quantity discharge valve to the soup server body.

FIG. 2 is a sectional view showing an embodiment of the present invention. It shows the state immediately after the removal of the clamps.

FIG. 3 is a sectional view showing an embodiment of the piston according to the present invention.

FIG. 4 is a sectional view showing the cylinder according to the present invention.

FIG. 5 is a sectional view showing the fixed quantity discharge valve body according to the present invention.

FIG. 6(A) is a frontal view and (B) is a longitudinal view of an embodiment of sealing the discharge outlet according to the present invention.

FIG. 7 is a sectional view showing the state before connecting the clamps and the piston shaft according to the present invention.

FIG. 8 is a sectional view showing the state of holding the piston shaft of the clamps according to the present invention.

DESCRIPTION OF THE CODES

1. Fixed quantity cutout valve proper

2. Suction inlet

3. Discharge outlet

5. Discharge nozzle

6. Cylinder

7. Piston body

8. Through hole formed in the cylinder

13. Cylindrical Teflon seal

19. Piston shaft

21. Short cylindrical Teflon seal

22. Short cylindrical seal pressure bar

25. Clamps

26. Rack gear

28, 28′. Piston clamps

34, 34′. Opening members

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We will now describe the preferred embodiments of the present invention with reference to drawings.

As shown in FIG. 2 and FIG. 5, the fixed quantity cut-down pump body 1 has a suction inlet (suction opening) 2 and a discharge outlet (discharge opening) 3 linked with the lower opening of the container for fluid 51 to be subdivided and filled and is formed in a cylindrical body whose top is closed with a front lid 4. In the above embodiment, the discharge outlet 3 is formed facing the top opening (suction inlet) 2, and the discharge outlet 3 is connected with a discharge nozzle 5.

The inner cylinder (cylinder) 6 shown in FIG. 4 is rotatably fixed to the fixed quantity cutout valve proper 1. Within the cylinder 6, the piston body 7 shown in FIG. 3 is slidably fixed.

In the cylinder 6, a through hole 8 is formed, and when the through hole 8 is connected with the suction inlet 2 of the fixed quantity cutout valve proper 1, the piston body 7 moves backward and fills the cylinder 6 with a predetermined quantity of soup containing ingredients, and when the through hole 8 of the cylinder 6 is connected with the discharge outlet 3 of the fixed quantity cutout valve proper 1, the piston body 7 moves forward and discharges soup containing ingredients from the discharge outlet connected therewith.

As shown in FIG. 5, a discoidal Teflon seal 9 is fixed on the front lid 4, and the periphery of the Teflon seal 9 is pressed against an O ring 10 so that no soup liquid may leak from the part in contact of the front lid 4.

The inner surface of the fixed quantity cutout valve proper 1 made of stainless steel is finished with hard chrome 12. However, when the hydraulic pressure in the hopper 51 connected with the suction inlet 2 rises, due to a straight contact surface with the cylinder (the stainless steel outer surface is finished with hard chrome) 6, some leakage may occur depending on the type of soup.

In the present invention, as shown in FIG. 5 and FIG. 6, as a cylindrical Teflon seal 13 formed in a curved surface 14 whose top can be brought into close contact with the cylinder at the discharge outlet 2 of the fixed quantity cutout valve proper 1 and the top end 14 of the flange 15 of the Teflon seal 13 is brought into tight contact with the cylinder 6 by the pressure given by the discharge nozzle 5, the leakage of soup liquid from the discharge outlet 3 is effectively prevented. Incidentally, the opening of the Teflon seal 13 is made larger than the through hole 8 of the cylinder 6. The code 16 shown in FIG. 5 represents a nozzle fixing metal fixture.

As FIG. 3 shows, the piston body 7 according to the present invention is made hollow inside 17 and the top surface is formed in a convex gently curved shape 18 in order to reduce its weight. Therefore, as it is not in tight contact with the Teflon sheet 9, torque is reduced when the piston moves backward and at the same time the trouble of ingredients being pinched in the space between the Teflon sheet 9 and the top surface of the piston 18 is reduced. The piston body 7 may be formed by stainless steel or other metals, or may be formed by a synthetic resin such as Teflon in order to reduce its weight.

A concave tapped hole is formed on the rear end surface of the piston body 7, and the top of the piston shaft 19 can be fitted into the tapped hole.

The rear end part of the piston body 7 is formed in a slightly smaller diameter, and a Teflon seal 21 formed in a taper 23 consisting of a bore diameter of the short cylindrical body gradually expanding in the forward direction and a short cylindrical seal pressure metal fixture (seal holder) 22 are fitted on the smaller diameter part. An end of the short cylindrical seal pressure metal fixture 22 is formed on the wall surface 48 having a hole for the insertion of the piston shaft for fitting.

The stepped part of the piston body 7 in contact with the taper 23 of the short cylindrical Teflon seal 21 is formed in a taper 20 rising in the forward direction. The top of the Teflon seal 21 may be made slightly protruding from the periphery of the piston body 7 by the pressure given to the Teflon seal 21 from behind by the short cylindrical seal pressure metal fixture 22 fitted on the piston shaft. Incidentally, in case of dismantling for cleaning, the piston may be easily pulled out of the cylinder by making the seal pressure metal fixture 22 move slightly backward. The pressure of the wall surface 48 by the seal pressure metal fixture 22 is given and adjusted by screwing the nut 24 fitted on the piston shaft 19.

As FIGS. 1 and 7 show, the rear end of the piston shaft 19 is held detachably by the clamp 25.

As FIG. 7 shows, the clamp 25 includes a fixing member 27 fixed on the rack gear 26, a piston clamps 28 and 28′ fixed rotatably facing the fixing member, a leaf spring (an elastic body) 29 giving impetus forward in the closing direction to the piston clamp, hook-shaped holding units 30 and 30′ for holding detachably the rear end of the piston shaft formed on both ends of the piston clamp, tapers 31 and 31′ expanding gradually in the forward direction formed in the surface opposite to the top ends of the holding units, a coil spring 33 to which the rear end of the piston shaft is brought into contact through a piston extrusion supporting fixture 32, and opening members 34 and 34′ having tapers 35 and 35′ guiding upward the top end of the piston clamp to open.

In the embodiment described above, the rack gear 26 is designed to move forward and backward being engaged with a pinion fixed on the rotary shaft of the motor. And the tapers 35 and 35′ of the opening member is also formed in a shape expanding gradually in the forward direction and has the same slope with the tapers 31 and 31′ of the surface opposite to the top end of the holding unit.

As FIG. 8 shows, the piston clamps 28 and 28′ with their top being in the closed state hold the rear end of the piston shaft 19, and the rack gear 26 moves forward and backward causing the piston to reciprocate from the limit of forward movement to the limit of the backward movement and the vice versa.

For removing the piston shaft 19 from the piston clamps 28 and 28′, the rack gear is made to move forward causing the fixing member 27 and piston clamps 28 and 28′ to move forward slightly further beyond the limit of forward movement. By taking such a measure, as FIG. 2 shows, the piston shaft 19 compresses the coil spring 33 through the action of the piston extrusion supporting fixture 32, and the tapers 31 and 31′ of the piston clamps rise being guided in contact with the tapers of the opening member 35 and 35′, the tops of the piston clamps open leading to the separation of the piston shaft 19 and the piston clamps 28 and 28′.

The piston clamps 28 and 28′ and the fixing member 27 are fixed rotatably at fixing points (lock pin of the piston clamps) 37 and 37′ backward from the center of the piston clamps, and a leaf spring 29 giving impetus forward to the piston clamps in the closing direction taking the fixing points 37 and 37′ as their supporting points is placed between the piston clamps backward from the supporting points 37 and 37′ and the fixing member. Incidentally, the leaf spring 29 is formed in the shape of a loop having a dog-legged section.

A housing chamber 49 for housing coil springs 33 is formed in front of the fixing member 27, and at the opening at the top end of the housing chamber 49 a piston shaft extruder 32 to which an impetus is given by a coil spring 33 is pressed and held by the force of the spring at its flange. The rear end of the piston shaft 19 is in contact with the piston shaft extruder 32 and the coil spring can be compressed by applying a pressure on the piston shaft extruder 32 and by overcoming the power of the spring.

As FIG. 4 shows, a 180° rotary guide groove (a 180° long hole) 38 is formed on the periphery of the cylinder 6, and a rotary valve stopper 39 shown in FIG. 5 is located on the guide groove 38 for positioning when the cylinder 6 begins rotating.

Large and small protrusions facing each other are formed at the top of the rotary cutout valve clutch body 40, and both protrusions are designed to fit with large and small clank claw holes 41, 42 shown in FIG. 8(B). Their different sizes are intended to facilitate positioning. The coil springs 43 shown in FIGS. 2 and 8 are designed to press the clutch body 40 to the cylinder 6. The code 50 shown in FIG. 2 represents a clank key, and 44 and 45 represent gears for rotating the cylinder.

The code 49 in FIG. 2 represents an encoder, which is directly connected with the encoder driven motor 47 to detect the number of output pulse wave forms of the encoder and to freely control the discharge amount (stopping position).

For connecting the clamp of the present invention, it is enough to make the rack gear move forward and to make the clutch move forward while the fixed quantity discharge valve is left on the server set stand. And for removing the clamp, it is enough to move it further forward slightly beyond the limit of forward movement as shown in FIG. 2, and to make the rack gear move backward to separate both of them. Therefore, the clamps can be detached automatically. 

1. A fluid subdividing and filling device in which a piston is moved backward to fill a fluid to be subdivided and filled into a cylinder, and the piston is moved forward to discharge said fluid, characterized in that a rear end portion of a piston body fitted slidably in said cylinder is formed to be somewhat smaller so that a short cylindrical seal is fitted, said short cylindrical seal is formed to have a taper in which an end inner circumference of a short cylindrical plate is spread open, a shoulder portion of the cylinder in contact with said taper is formed in a taper that rises in the forward direction, a short cylindrical seal holder is fitted from backward of said short cylindrical Teflon seal, said short cylindrical Teflon seal is pressed forward, whereby the extreme end of said short cylindrical Teflon seal is projected somewhat from a piston body outer circumference.
 2. The fluid subdividing and filling device according to claim 1 comprising a fixed quantity cut-down pump body having an suction opening in communication with an lower-end opening of a liquid food accommodating container for subdividing and filling and a discharge opening to a subdividing and filling container, a cylinder turnably fitted in the fixed quantity cut-down pump body, a piston sidably fitted in the cylinder, and a through-hole formed in the cylinder, wherein rotation of the cylinder and advance/backward movement of the piston are coupled so that the through-hole of the cylinder is communicated with the suction opening of the fixed quantity cut-down pump body, the piston moves back to fill a fixed quantity of liquid food into the cylinder whereas when the through-hole of the cylinder is communicated with the discharge opening of the apparatus body, the piston advances to discharge liquid food from the discharge opening communicated
 3. The fluid subdividing and filling apparatus according to claim 2 wherein the discharge opening of the apparatus body is fitted with a cylindrical Teflon seal formed in a curved surface whose top can get into a tight contact with said cylinder and the top opening of said Teflon seal is brought into tight contact with the cylinder to cover said through hole.
 4. A piston wherein the rear end portion of a piston body fitted slidably in said cylinder is formed to be somewhat smaller so that a short cylindrical seal is fitted, said short cylindrical seal is formed to have a taper in which an end inner circumference of a short cylindrical plate is spread open, a shoulder portion of the cylinder in contact with said taper is formed in a taper that rises in the forward direction, a short cylindrical seal holder is fitted from backward of said short cylindrical Teflon seal, said short cylindrical Teflon seal is pressed forward, whereby the extreme end of said short cylindrical Teflon seal is projected somewhat from a piston body outer circumference.
 5. The piston according to claim 4 wherein the top of said piston body is formed in a convex gentle curved shape.
 6. The piston according to claim 5 wherein a concave tapped hole is formed on the rear end surface of the body of said piston, the top of the piston shaft is screwed into said tapped hole and a nut that had been screwed on said piston shaft is further screwed and clamped fast to press the rear end surface of said seal holder that had been fitted on the piston shaft.
 7. A fluid subdividing and filling device for filling the cylinder with fluid to be subdivided and filled by making the piston move backward and for discharging said fluid by making the piston move forward, comprising a fixing member fixed on the means for making the piston move forward and backward, a piston clamp rotatably fixed on the opposite side of said fixing member, an elastic body for giving impetus to said piston clamp to move forward in the closing direction, a holding unit for holding detachably the rear part of a piston shaft formed on both ends of said piston clamps, a taper expanding gradually forward formed in the surface opposite to said holding unit, an elastic body to which the rear end of said piston shaft enters into contact directly or through other members, and an opening member having tapers guiding upward in such a way that the top tapers of the holding unit of said piston clamps may open, wherein a forward movement of said fixing member resulting in a forward movement of the piston clamps further forward beyond the limit of forward movement leads to the compression of said elastic body by said piston shaft, and the tapered top of said holding unit of said piston clamps, being guided in contact with the taper of said opening member, opens leading to the separation of the piston shaft and the piston clamp.
 8. A clamp for linking the piston shaft and the means for making the piston move forward and backward comprising a fixing member fixed on the means for making the piston move forward and backward, a piston clamp fixed rotatably facing said fixing member, an elastic body giving impetus to said piston clamp forward in the closing direction, a holding unit for holding detachably the rear end of the piston shaft formed on both ends of said piston clamp, a taper expanding gradually forward formed on the opposite surface to the top of said holding unit, an elastic body to which the rear end of said piston shaft is in contact directly or through another member, and an opening member with a taper guiding upward opens the top taper of the holding unit of said piston clamps, wherein a forward movement of said fixing member resulting in a forward movement of the piston clamp further beyond the limit of forward movement leads to the compression of said elastic body by said piston shaft, and the tapered top of said holding unit of said piston clamp, being guided in contact with the taper of said opening member, opens leading to the separation of the piston shaft and the piston clamps.
 9. The clamp according to claim 8 wherein the means for making said piston move forward and backward is a rack gear engaged with a pinion fixed on the rotating shaft of the motor.
 10. The clamp according to claim 9 wherein said piston clamp and said fixing member are rotatably fixed behind the center of the piston clamp and an elastic body for giving impetus to the piston clamp forward in the closing direction taking the fixing point as an a supporting point is placed between the piston clamps behind said supporting point and said fixing member.
 11. The clamp according to claims 10 wherein a housing unit for housing the elastic body is formed in front of said fixing member, a piston shaft extruder given impetus by said elastic body is placed in the opening in front of said housing unit and the rear end part of said piston shaft is brought into contact with said piston shaft extruder, 